From the DE-OS 27 48 452 is known a bone milling tool for round milling a hip joint head which is provided with a central hole into which a centering pin is inserted. The milling head is joined to a driveshaft which is,. at least near the area of the milling head, of tubular design.
Also known is a bone milling tool as illustrated in FIG. 4. A bone milling tool of this type is used for precisely fitting preparation of bones, in particular tubular bones. It is important, in particular with cementfree implantation of prosthesis, to create an extremely precisely fitting bone bed to accommodate the prosthesis, on the one hand to ensure the largest possible contact surface for fast grafting of the bone and on the other hand to eliminate micro movements. Rotary instruments are preferred as the precision of oscillating saws is insufficient.
Bone milling tool 10a illustrated in FIG. 4 is a front-end milling tool. It is composed of a cylindrical milling head 12a with cutting teeth configured at the front. A guide pin 30 is also arranged at this side. A driveshaft 14' is mounted to the rear of milling head 12a. When using this bone milling tool 10a, guide pin 30 is pushed into a guide bore which has been entered into the bone, thus ensuring guided and directionally stable processing. Exerting pressure (see arrows 26 in FIG. 4) onto driveshaft 14' in the direction of guide pin 30 establishes contact of front-end cutting teeth with the bone and mills a rotary-symmetrical surface into the depth.
The problem with both of the aforedescribed bone milling tools lies with the respective driveshaft, which protrudes from the field of operation and has to be connected to a drive unit. If the field of operation is small and access has to be of narrow design for anatomical or surgical reasons, then it can happen that, whilst milling downwards, the driveshaft is forced out of its direction by protrusions in the field of operation, which results in a directionally unstable or directionally incorrect milling surface. The result is an inaccurate bone bed, both relative to the contact surface and relative to positioning of a prosthesis.